[Elecraft] Antenna Problems with K3 firmware 5.57

[Walter Underwood]

Use a series-tuned “wave trap” on KLIV’s frequency across your feedline. That will short out the feedline at that frequency. It will add some inductive load above the resonant frequency, but the ATU can deal with that.

The components need to be rated for the transmission line voltages, but they probably won’t be handling a lot of current.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Mar 31, 2017, at 2:36 PM, Bill Frantz <frantz at pwpconsult.com> wrote:
> 
> I have a 160M full length dipole. The center used to be at about 40 feet. About the time version 5.57 of the firmware came out, the mast supporting the center feed point broke and I re-rigged with the center at about 22 feet. (I hate debugging when there were two changes.)
> 
> Measurement of the lowered antenna with a MFJ-259B antenna analyzer show 1.2:1 SWR match at 1.87 KHz with 2,5:1 and 3.3:1 at the band edges from the shack. Because of the mismatch at the band ends, I usually use the antenna using the KAT3A tuner installed in my K3. (I don't have similar figures for the higher antenna, but the SWR curve matches the computer model.)
> 
> I used the antenna with modest success including 10 DXCCs and 41 US states confirmed.
> 
> When I installed 5.57, I noticed significant power drops on 160M, stepping down from 100W to 25W and 50W. With the help of Elecraft support, we have concluded that the antenna is irritating the new firmware feature:
> 
>    K3 MCU 5.57 / DSP 2.88 / FPF 1.26, 2-16-2017
> 
>    * FASTER RESPONSE TO HIGH REFLECTED POWER. The transceiver will now reduce
>    drive more quickly when transient conditions cause excessive reflected
>    power. This roll-back response does not change the set power level (PWR
>    knob); instead, it reduces the drive to get below the reflected power
>    limit. This means that once a better match is restored (such as when using
>    an antenna tuner), the set power level will automatically be restored.
> 
> When I backed off to version 5.50, 160M performance seems to have gone back to what it was.
> 
> Measuring the open-circuit voltage on the antenna feed line with a oscilloscope shows about 600mV peak to peak. I estimate, based on eyeballing the trace and measuring other antennas, that about 200mV of that is 60 cycle hum. Elecraft support thinks this is enough voltage to affect the internal K3 SWR bridge.
> 
> The voltage is most likely from AM broadcast stations. The strongest station, measured with the P3, is KLIV (5000W) about 8 miles from my QTH.
> 
> 
> So now, the question is what to do about the problem. Several things I have been able to think of are:
> 
> * Use a broadcast band filter. DXEngineering has one that will handle 200W, but it wants 50 ohms impedance on both ends. Therefore it is recommended to install it between the power amp (internal to the K3) and the tuner (also internal to the K3). I might be tempted to insert one in the K3, but the tuner and power amp are connected through a header, not a simple cable I could reroute to install the filter.
> 
> * Get a KAT500 and the filter. Expensive, but straight forward.
> 
> * Sometimes the power remains at 100W when the internal tuner is in bypass mode, but not always. It might remain stable enough for QSO, but flipping back and fourth seems to be a pain.
> 
> Does anyone have any suggestions?
> 
> Thanks - Bill AE6JV
> 
> -----------------------------------------------------------------------
> Bill Frantz        | Concurrency is hard. 12 out  | Periwinkle
> (408)356-8506      | 10 programmers get it wrong. | 16345 Englewood Ave
> www.pwpconsult.com |                - Jeff Frantz | Los Gatos, CA 95032
> 
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